Deterioration analysis method

ABSTRACT

The present invention provides deterioration analysis method which allows a detailed analysis of deterioration, especially deterioration of surface conditions, of a polymer material. The present invention relates to a deterioration analysis method, including irradiating a polymer material with high intensity X-rays, and measuring X-ray absorption while varying the energy of the X-rays, to analyze deterioration of the polymer.

TECHNICAL FIELD

This application is a divisional of co-pending U.S. patent applicationSer. No. 13/881,158 filed on Apr. 24, 2013, which is the national phaseof PCT International Application No. PCT/JP2011/068139 filed on Aug. 9,2011, which claims the benefit of Japanese Patent Application No.2011-167131 filed on Jul. 29, 2011 and Japanese Patent Application No.2010-281017 filed on Dec. 16, 2010. The entire contents of all of theabove applications are hereby incorporated by reference.

The present invention relates to a deterioration analysis method foranalysis of deterioration of a polymer material.

BACKGROUND ART

For analyzing a change in chemical state of a polymer materialcontaining at least one diene rubber caused by deterioration, forexample, an infrared spectroscopy (FT-IR), nuclear magnetic resonanceanalysis (NMR), and X-ray photoelectron spectroscopy (XPS) and the likeare commonly employed. Though FT-IR or NMR allows a detailed analysis ofthe chemical state, the obtained information is bulk information andtherefore it is difficult to analyze in detail the chemical state afterdeterioration which starts at a sample surface.

On the other hand, XPS is a surface-sensitive method and is thereforethought to be effective for analysis of a change in chemical statecaused by deterioration. As one example of analysis and evaluation ofdeterioration by XPS, FIG. 1 shows the results of XPS measurement of theis orbital of carbon in fresh butadiene rubber (BR) , ozone-deterioratedBR, and oxygen-deteriorated BR (carbon K-shell absorption edge of BR).

As shown in FIG. 1, in the XPS measurement, the peak of C═C bond (doublebond) and the peak of C—C bond (single bond) overlap each other ataround 285 eV, and therefore the chemical states of the different groupscannot be distinguished. Hence, it is difficult to determine the amountof C═C bonds (double bonds) that is reduced by deterioration. Moreover,in FIG. 2 showing the results of XPS measurement of the oxygen K shellabsorption edge of BR, no difference is found in the spectra between theozone-deteriorated BR and oxygen-deteriorated BR. Hence, a detailedanalysis of deterioration by XPS is difficult.

Meanwhile, measurement of X-ray absorption spectra of polymers has alsobeen carried out as disclosed in Non Patent Literatures 1 to 3. However,no disclosure is found in any literatures including these non patentliteratures that deterioration factors can be distinguished based on theX-ray absorption spectra.

CITATION LIST Non Patent Literature

Non Patent Literature 1: O. Dhez, H. Ade, S. G. Urquhart. J. ElectronSpectrosc. Relat. Phenom., 2003, 128, 85-96

Non Patent Literature 2: Robert J. Klein, Daniel A. Fischer, and JosephL. Lenhart. Langmuir., 2008, 24, 8187-8197

Non Patent Literature 3: Toshihiro Okajima, Hyomen kagaku (SurfaceScience), 2002, Vol. 23, No. 6, 356-366

SUMMARY OF INVENTION Technical Problem

The present invention aims to provide a deterioration analysis methodwhich can solve the above problems and allows a detailed analysis ofdeterioration, especially deterioration of surface conditions, of apolymer material.

Solution to Problem

The present invention relates to a deterioration analysis method,including irradiating a polymer material with high intensity X-rays, andmeasuring X-ray absorption while varying the energy of the X-rays, toanalyze deterioration of the polymer.

The polymer material is preferably a rubber material containing at leastone diene rubber, or a composite material combining the rubber materialand at least one resin.

The high intensity X-rays preferably have a number of photons of 10⁷(photons/s) or more and a brilliance of 10¹⁰ (photons/s/mrad²/mm²/0.1%bw) or more. Also, an energy range scanned with the high intensityX-rays is preferably 4000 eV or less.

The deterioration analysis method preferably includes: calculatingnormalization constants α and β using Equation 1 below based on X-rayabsorption spectra obtained by scanning over a required range of highintensity X-ray energies at the carbon K-shell absorption edge withinthe range of 260 to 400 eV; performing waveform separation of the X-rayabsorption spectra at the carbon K-shell absorption edge corrected withthe normalization constants α and β to obtain peak areas attributed ton* transition at around 285 eV; and determining a degree ofdeterioration using Equation 2 below with the obtained peak areas:

[total area of X-ray absorption spectrum over measurement range ofsample before deterioration]×α=1,

and

[total area of X-ray absorption spectrum over measurement range ofsample after deterioration]×β=1;

and   (Equation 1)

[1−[(peak area of n* after deterioration)×β]/[(peak area of n* beforedeterioration)×α]]×100=degree (%) of deterioration. (Equation 2)

In the deterioration analysis method, peak intensities may be usedinstead of the peak areas.

The deterioration analysis method preferably includes: performingwaveform separation of an X-ray absorption spectrum at the oxygenK-shell absorption edge obtained by scanning over a range of highintensity X-ray energies of 500 to 600 eV; and calculating contributionrates of oxygen deterioration and ozone deterioration using Equation 3below, wherein the oxygen deterioration corresponds to a peak on the lowenergy side with a peak top energy in the range of 532 to 532.7 eV, andthe ozone deterioration corresponds to a peak on the high energy sidewith a peak top energy in the range of 532.7 to 534 eV:

[peak area of oxygen deterioration]/[(peak area of ozone deterioration)(peak area of oxygen deterioration)]×100=contribution rate (%) of oxygendeterioration,

and

[peak area of ozone deterioration]/[(peak area of ozonedeterioration)+(peak area of oxygen deterioration)]×100=contributionrate (%) of ozone deterioration.   (Equation 3)

In the deterioration analysis method, peak intensities may be usedinstead of the peak areas.

The deterioration analysis method preferably includes: determining anormalization constant γ using Equation 4 below based on an X-rayabsorption spectrum at the carbon K-shell absorption edge afterdeterioration; and correcting a total peak area of the oxygen K-shellabsorption edge with the normalization constant γ to determine theamount of oxygen and ozone bonded to the polymer material:

[total area of X-ray absorption spectrum at carbon K-shell absorptionedge]×γ=1,

and

[peak area of oxygen K-shell absorption edge]×γ=amount (index) of oxygenand ozone bonded.   (Equation 4)

ADVANTAGEOUS EFFECTS OF INVENTION

Since the deterioration analysis method according to the presentinvention includes irradiating a polymer material with high intensityX-rays, and measuring X-ray absorption while varying the energy of theX-rays, to analyze deterioration of the polymer, the method can analyzein detail the deterioration, especially deterioration of surfaceconditions, of a polymer material. Accordingly, with regard to thedeterioration of a polymer material, the degree (%) of deterioration,the contribution rates of oxygen deterioration and ozone deterioration,and the amount of oxygen and ozone bonded to the polymer material(deterioration indicator) can be measured.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the results of XPS measurement of the isorbital of carbon in fresh butadiene rubber (BR), ozone-deteriorated BR,and oxygen-deteriorated BR.

FIG. 2 is a graph showing the results of XPS measurement of the oxygenK-shell absorption edge in ozone-deteriorated butadiene rubber andoxygen-deteriorated butadiene rubber.

FIG. 3 is a graph (before normalization) showing the results of NEXAFSmeasurement of the carbon K-shell absorption edge in fresh butadienerubber, a sample subjected to ozone deterioration for seven hours, and asample subjected to oxygen deterioration for a week.

FIG. 4 is a graph (after normalization) showing the results of NEXAFSmeasurement of the carbon K-shell absorption edge in fresh butadienerubber, a sample subjected to ozone deterioration for seven hours, and asample subjected to oxygen deterioration for a week.

FIG. 5 is a graph showing the results of NEXAFS measurement around theoxygen K-shell absorption edge in a butadiene rubber sample subjected toozone deterioration for seven hours and a sample subjected to oxygendeterioration for a week.

FIG. 6 is a graph showing the results of NEXAFS measurement around theoxygen K-shell absorption edge in a butadiene rubber sample subjected tocomplex deterioration (both oxygen deterioration and ozonedeterioration).

FIG. 7 is a graph (after normalization) showing the results of NEXAFSmeasurement in butadiene rubber samples subjected to ozone deteriorationfor one hour and seven hours.

DESCRIPTION OF EMBODIMENTS

The deterioration analysis method of the present invention includesirradiating a polymer material with high intensity X-rays, and measuringX-ray absorption while varying the energy of the X-rays, to analyzedeterioration of the polymer. Known deterioration factors of polymermaterials such as rubber include deterioration of polymer molecularchains and crosslinked structures by ultraviolet light, oxygen, ozone,heat and the like. To improve the resistance to deterioration, it isimportant to know what factor is responsible and how the polymermolecular chains and crosslinked structures then change.

In this respect, the deterioration analysis method focuses on the use ofhigh intensity X-rays to analyze the chemical state in greater detailthan the conventional methods such as FT-IR, NMR, Raman scatteringspectroscopy, and XPS. In this method, while the energy of highintensity X-rays is varied, fresh and deteriorated polymer materials areirradiated with the X-rays to measure the X-ray absorption, and then theobtained spectra are compared, whereby the deterioration of thedeteriorated polymer material can be analyzed.

Specifically, a method may be employed in which an X-ray absorptionspectrum around the absorption edge of a specific target element ismeasured using high intensity X-rays (NEXAFS: Near Edge X-ray AbsorptionFine Structure). Since the soft X-ray region includes absorption edgesof light elements, the chemical state of soft materials can be analyzedin detail.

Since X-ray energy is used for scanning in the NEXAFS method, acontinuous X-ray generator is needed as the light source. For a detailedanalysis of the chemical state, an X-ray absorption spectrum with highS/N and S/B ratios needs to be measured. For this reason, a synchrotronis suitably used in the NEXAFS measurement because it emits X-rayshaving a brilliance of at least 10¹⁰ (photons/s/mrad²/mm²/0.1% bw) andis a continuous X-ray source. It is to be noted that the symbol bwindicates a bandwidth of X-rays emitted from a synchrotron.

The brilliance (photons/s/mrad²/mm²/0.1% bw) of the high intensityX-rays is preferably 10¹⁰ or more, and more preferably 10¹² or more. Theupper limit thereof is not particularly limited, and the X-ray intensityused is preferably low enough not to cause radiation damage.

The number of photons (photons/s) of the high intensity X-rays ispreferably 10⁷ or more, and more preferably 10⁹ or more. The upper limitthereof is not particularly limited, and the X-ray intensity used ispreferably low enough not to cause radiation damage.

The energy range scanned with the high intensity X-rays is preferably4000 eV or less, more preferably 1500 eV or less, and still morepreferably 1000 eV or less. With an energy range exceeding 4000 eV, thedeterioration of a target polymer composite material may not beanalyzed. The lower limit is not particularly limited.

The measurement can be carried out as follows. A sample placed in anultra-high vacuum is irradiated with soft X-rays so that photoelectronsare emitted. Then electrons flow from the ground to the sample so as tocompensate for the emitted photoelectrons, and this sample current ismeasured. Accordingly, such measurement is surface-sensitive but canonly measure samples that do not produce gas in vacuo and areelectrically conductive. Therefore, in the past, crystals and molecularadsorption have been mainly studied through the measurement, whereasrubber samples that are likely to produce gas and are insulatingmaterials have hardly been studied.

However, the ESCA method, which is similarly surface-sensitive, observesthe inner shells of an atom and thus is difficult to distinguish thedeteriorations of a polymer in detail. In contrast, the NEXAFS methodobserves the outer shells of an atom which are affected by the reactionbetween atoms, and thus allows greater reflection of the impact of anelement bonded to the target element than the ESCA method. Therefore,the present inventors have considered that the NEXAFS method candistinguish individual molecular states and thus can distinguishdeterioration factors, thereby completing the present invention.

More specifically, the measurement can be conducted by the followingmethod.

A sample mounted on a sample holder is placed in a vacuum chamber forX-ray absorptiometry. Then the sample is irradiated with continuousX-rays that are emitted from a synchrotron and subsequentlymonochromatized with a monochromator. At that time, secondary electronsand photoelectrons escape from the sample surface into vacuum, and thenelectrons are replenished from the ground to compensate for the loss ofelectrons. Then, the X-ray absorption (μL) is calculated using Equation5 below, wherein the X-ray absorption intensity I represents a currentflowing from the ground, and the incident X-ray intensity I₀ representsa current from a gold mesh provided in an optical system of a beamline(electron yield method). It should be noted that the equation ofLambert-Beer is applicable to the method, and Equation 5 is thought tohold approximately in the case of the electron yield method:

I ₀(E)/I(E)=exp(μL)≅μL (E: energy of X-rays, L: thickness of sample, μ:absorption coefficient).   (Equation 5)

The following three methods are typically used as the NEXAFSmeasurement. In examples of the present invention, the electron yieldmethod is employed but is not intended to limit the scope of theinvention. Various detection methods may be employed and may be combinedfor simultaneous measurement.

(Transmission Method)

This is a method of detecting the intensity of the X-rays having passedthrough a sample. For measurement of the intensity of transmitted light,for example, a photodiode array detector may be used.

(Fluorescence Method)

This is a method of detecting fluorescent X-rays generated when a sampleis irradiated with X-rays. In the case of the transmission method, ifthe X-ray absorption of an element contained in a small amount in asample is measured, then a spectrum with a poor S/B ratio is obtainedbecause the signal is small and the background is high due to X-rayabsorption by an element contained in a large amount in the sample. Incontrast, in the case of the fluorescence method (especially when anenergy dispersive detector or the like is used), only the fluorescentX-rays from the target element can be measured and thus the elementcontained in a large amount has a small influence. Hence, the method iseffective in order to measure the X-ray absorption spectrum of anelement contained in a small amount. In addition, since fluorescentX-rays have high penetrating power (low interaction with substances),fluorescent X-rays generated inside the sample can be detected. Hence,the method is the second most suitable method for obtaining bulkinformation after the transmission method.

(Electron Yield Method)

This is a method of detecting a current flowing when a sample isirradiated with X-rays. Thus, the sample needs to be an electricallyconductive material. Since polymer materials are insulating materials,X-ray absorption measurement of a polymer material has mostly beencarried out by putting a very thin layer of a sample on a substrate bydeposition, spin-coating or the like. In the present invention, when apolymer material is processed (cut) with a microtome to 100 μm or less,preferably to 10 μm or less, more preferably to 1 μm or less, and stillmore preferably to 500 nm or less, high S/B and S/N ratios can beachieved through the measurement.

The electron yield method features surface sensitivity (information fromthe sample surface to a depth of approximately several nanometers).Irradiation of a sample with X-rays causes escape of electrons fromelements. Since electrons have a great interaction with substances,their mean free path in a substance is short.

The X-ray absorption spectra of a polymer material can be measured bythe electron yield method and then analyzed to assay the degree (%) ofdeterioration, the contribution rates (%) of oxygen deterioration andozone deterioration, and the amount of oxygen and ozone bonded(deterioration indicator). These assays are described below.

The deterioration analysis method may include: calculating normalizationconstants α and β using Equation 1 below based on X-ray absorptionspectra obtained by scanning over a required range of high intensityX-ray energies at the carbon K-shell absorption edge within the range of260 to 400 eV; performing waveform separation of the X-ray absorptionspectra at the carbon K-shell absorption edge corrected with thenormalization constants α and β to obtain peak areas attributed to n*transition at around 285 eV; and determining a degree of deteriorationusing Equation 2 below with the obtained peak areas:

[total area of X-ray absorption spectrum over measurement range ofsample before deterioration]×α=1,

and

[total area of X-ray absorption spectrum over measurement range ofsample after deterioration]×β=1;

and   (Equation 1)

[1−[(peak area of n* after deterioration)×β]/[(peak area of n* beforedeterioration)×α]]×100=degree of deterioration (%).   (Equation 2)

In this manner, the degree (%) of deterioration of a polymer afterdeterioration can be obtained to allow analysis of the deteriorationrate. In the method for determining the degree of deterioration, therange of high intensity X-ray energies is preferably 260 to 350 eV. Inthe method for determining the degree of deterioration, the backgroundis assessed based on a slope before the absorption edge and subtracted,prior to the calculation of Equation 1.

In the method for determining the degree of deterioration, the totalarea of the X-ray absorption spectrum in Equation 1 is the integral ofthe spectrum over a measurement range. The energy range can be changedaccording to the measurement conditions and the like.

The method for determining the degree of deterioration is morespecifically described using an example in which fresh BR, a samplesubjected to ozone deterioration for seven hours, a sample subjected tooxygen deterioration for a week are used.

FIG. 3 shows the results of NEXAFS measurement of the carbon K-shellabsorption edge in these samples. As shown in FIG. 3, deterioratedsamples each have a smaller n* peak at around 285 eV than the freshsample; however, the NEXAFS method is difficult to perform an absolutemeasurement because subtle changes in the distance from the light sourceto the sample and the like affect the magnitude of the X-ray absorptionspectrum. For this reason, the results of NEXAFS measurement of thecarbon K-shell absorption edge cannot be simply compared betweensamples.

For comparison between the X-ray absorption spectra of the measuredsamples, normalization is carried out as follows (the X-ray absorptionspectrum of each sample is corrected for direct comparison) . Since theamount of carbon shell X-ray absorption is not changed before and afterdeterioration, the peak area of the carbon K-shell absorption edge isnormalized to 1 using Equation 1. In other words, normalizationconstants α and β are first calculated using Equation 1 based on theX-ray absorption spectra before normalization, and then the spectra arecorrected (normalized) by multiplying the X-ray absorption spectrabefore normalization by α and β, whereby the n* peaks of the samples canbe directly compared.

FIG. 4 shows the thus-obtained spectra at the carbon K-shell absorptionedge after normalization. The degree of deterioration is determinedusing Equation 2 based on the normalized spectra. The degree ofdeterioration is the n*peak reduction from before to afterdeterioration, and indicates the deterioration rate (%) of a sample.

In the method for determining the degree of deterioration, the degree ofdeterioration can be similarly determined when peak intensities are usedinstead of the peak areas in Equation 2.

Other examples of the deterioration analysis method include a methodthat includes: performing waveform separation of an X-ray absorptionspectrum at the oxygen K-shell absorption edge obtained by scanning overa range of high intensity X-ray energies of 500 to 600 eV; andcalculating contribution rates of oxygen deterioration and ozonedeterioration using Equation 3 below, wherein the oxygen deteriorationcorresponds to a peak on the low energy side with a peak top energy inthe range of 532 to 532.7 eV, and the ozone deterioration corresponds toa peak on the high energy side with a peak top energy in the range of532.7 to 534 eV:

[peak area of oxygen deterioration]/[(peak area of ozone deterioration)+(peak area of oxygen deterioration)]×100=contribution rate (%) ofoxygen deterioration,

and

[peak area of ozone deterioration]/[(peak area of ozone deterioration)+(peak area of oxygen deterioration)]×100=contribution rate (%) of ozonedeterioration.   (Equation 3)

In this manner, the contribution rates (%) of oxygen deterioration andozone deterioration in a polymer material after deterioration can beobtained to allow analysis of the contribution rate of eachdeterioration factor. In the method for calculating the contributionrates, the background is assessed based on a slope before the absorptionedge and subtracted, prior to the calculation of Equation 3.

The method for calculating the contribution rates is more specificallydescribed using an example in which fresh BR, a sample subjected toozone deterioration for seven hours, and a sample subjected to oxygendeterioration for a week are used.

First, FIG. 5 shows the results of NEXAFS measurement around the oxygenK-shell absorption edge in the fresh BR, the sample subjected to ozonedeterioration for seven hours, and the sample subjected to oxygendeterioration for a week as shown in FIG. 1. As shown in the figure, theozone-deteriorated sample has a peak at 532.7 to 534 eV, and theoxygen-deteriorated sample has a peak at 532 to 532.7 eV. It is foundout that, of these two peaks, the peak on the high energy side isattributed to ozone deterioration and the peak on the low energy side isattributed to oxygen deterioration.

FIG. 6 shows the results of NEXAFS measurement in a sample subjected tocomplex deterioration (both oxygen deterioration and ozonedeterioration) . As shown in FIG. 6, a peak with two shoulders wasdetected at 532 to 534 eV. This is thought to be due to overlapping ofthe peak on the low energy side (532 to 532.7 eV) attributed to oxygendeterioration and the peak on the high energy side (532.7 to 534 eV)attributed to ozone deterioration. Hence, peak separation was performedand then the contribution rates of oxygen deterioration and ozonedeterioration were determined using Equation 3. In this manner, thesample subjected to both oxygen deterioration and ozone deteriorationcan be analyzed for the proportion of each of the two deteriorationfactors, oxygen deterioration and ozone deterioration.

In the method for calculating the contribution rates, the contributionrates of oxygen deterioration and ozone deterioration can be similarlydetermined when peak intensities are used instead of the peak areas inEquation 3.

Still other examples of the deterioration analysis method include amethod that includes: determining a normalization constant γ usingEquation 4 below based on an X-ray absorption spectrum at the carbonK-shell absorption edge after deterioration; and correcting a total peakarea of the oxygen K-shell absorption edge with the normalizationconstant γ to determine the amount of oxygen and ozone bonded to thepolymer material:

[total area of X-ray absorption spectrum at carbon K-shell absorptionedge]×γ=1,

and

[peak area of oxygen K-shell absorption edge]×γ=amount (index) of oxygenand ozone bonded.   (Equation 4)

In this manner, the amount of oxygen and ozone bonded to a polymermaterial due to deterioration can be measured and used as adeterioration indicator.

In the method for determining the bonded amount, the total peak area isthe integral of the spectrum over a measurement range. The energy rangecan be changed according to the measurement conditions and the like.

The method for determining the bonded amount is more specificallydescribed using an example in which BR samples subjected to ozonedeterioration for an hour and seven hours are used.

FIG. 7 shows the results of NEXAFS measurement in these samples. Thesespectra are each obtained by calculating a normalization constant γusing Equation 4 based on an X-ray absorption spectrum at the carbonK-shell absorption edge, and carrying out normalization as mentionedabove. The normalized peak area of the oxygen K-shell absorption edge isthought to correspond to the amount of oxygen and ozone bonded. As shownin the figure, the sample subjected to deterioration for seven hoursshows a larger area than the sample subjected to deterioration for anhour, and therefore the resulting value can be used as a deteriorationindex. A larger number of the deterioration index indicates a largeramount of oxygen bonded to the polymer material due to deterioration. Inthis manner, the deterioration rate when oxygen and ozone are bonded toa polymer material can be measured based on the rate of increase in thepeak area of the oxygen K-shell absorption edge.

The method of the present invention mentioned above can be carried outusing, for example, the BL12 beamline at Kyushu Synchrotron LightResearch Center (SAGA-LS).

The polymer material usable in the present invention is not particularlylimited, and may be any conventionally known material. For example, thepolymer material may suitably be a rubber material containing at leastone diene rubber, or a composite material combining the rubber materialand at least one resin. Examples of the diene rubber include polymerscontaining a double bond, such as natural rubber (NR), isoprene rubber(IR), butadiene rubber (BR), styrene butadiene rubber (SBR),acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), butylrubber (IIR), halogenated butyl rubber (X-IIR), and styrene isoprenebutadiene rubber (SIBR).

The resin is not particularly limited, and may be a general purposeresin used in the rubber industry field. Examples thereof includepetroleum resins such as C5 aliphatic petroleum resins andcyclopentadiene petroleum resins. The deterioration analysis method ofthe present invention can suitably be applied to these materials.

EXAMPLES

The present invention is more specifically described referring to, butnot limited to, examples.

Examples and Comparative Examples

Deteriorated samples used in examples and comparative examples wereprepared using the rubber materials and deterioration conditionsmentioned below. For measurement by the NEXAFS method, each sample wasprocessed to have a thickness of 100 μm or less using a microtome. Then,to avoid any influence of oxygen other than that due to deterioration,the prepared samples were stored in a vacuum desiccator.

Rubber Materials

IR: Nipol IR 2200 from ZEON CORPORATIONBR: Ubepol BR 130B from UBE INDUSTRIES, LTD.SBR: Nipol 1502 from ZEON CORPORATIONSIBS: SIBSTAR 102T from Kaneka CorporationSample after driving in US: Tire that had been driven in US Sample afterdriving in Japan: Tire that had been driven in Japan

Deterioration Conditions

Ozone deterioration: 40° C., 50 pphm (1 hour or 7 hours)Oxygen deterioration: 80° C., oxygen:nitrogen=5:1 (168 hours)

Used Devices

NEXAFS: NEXAFS measurement device provided with the beamline BL12 atKyushu Synchrotron Light Research Center (SAGA-LS)

XPS: AXIS Ultra from Kratos Surface Analysis

The degree (%) of deterioration of each sample was determined throughthe following deterioration rate analysis with NEXAFS. Also, thecontribution rates (%) of oxygen and ozone deterioration were determinedthrough the following deterioration contribution rate analysis. Inaddition, the deterioration indicator (index) was determined through thefollowing deterioration indicator determination.

The measurement conditions of NEXAFS used here were as follows.

Brilliance: 5×10¹² photons/s/mrad²/mm²/0.1% bw

Number of photons: 2×10⁹ photons/s

Deterioration Rate Analysis

Scanning was performed over a range of high intensity X-ray energies of260 to 400 eV to obtain X-ray absorption spectra at the carbon K-shellabsorption edge. Normalization constants α and β were calculated usingEquation 1 based on the spectra over the required range of 260 to 350eV, and then the spectra were normalized (corrected) with the obtainedconstants. The normalized spectra were subjected to waveform separation,and then the degree (%) of deterioration was determined using Equation 2based on the resulting peak areas attributed to n* transition at around285 eV.

Deterioration Contribution Rate Analysis

Scanning was performed over a range of high intensity X-ray energies of500 to 600 eV to obtain an X-ray absorption spectrum at the oxygenK-shell absorption edge. The spectrum was subjected to waveformseparation, and then the contribution rates of oxygen deterioration andozone deterioration were calculated using Equation 3, wherein the oxygendeterioration corresponds to a peak on the low energy side with a peaktop at 532 to 532.7 eV, and the ozone deterioration corresponds to apeak on the high energy side with a peak top at 532.7 to 534 eV.

Deterioration Indicator Determination

The normalization constant γ was determined using Equation 4 based onthe X-ray absorption spectrum at the carbon K-shell absorption edgeafter deterioration obtained in the deterioration rate analysis. Thetotal peak area of the oxygen K-shell absorption edge was corrected(normalized) with the constant, whereby the amount of oxygen and ozonebonded to the polymer material (deterioration indicator) was determinedbased on Equation 4.

In Comparative Examples 1 to 4, the deteriorated samples were evaluatedusing XPS.

Table 1 shows the results obtained in the above analyses.

TABLE 1 Comparative Example 1 Example 1 Example 2 Example 3 Measurementmethod XPS NEXAFS NEXAFS NEXAFS Material name IR IR IR IR Deteriorationtime (h)/ozone 1 1 7 — Deterioration time (h)/hot oxygen — — — 168Contribution rate (%) of ozone deterioration Not calculable 100 100 0Contribution rate (%) of oxygen deterioration Not calculable 0 0 100Degree (%) of deterioration Not calculable 78 100 23 Deteriorationindicator Not calculable 0.43 0.56 0.22 Comparative Example 2 Example 4Example 5 Example 6 Measurement method XPS NEXAFS NEXAFS NEXAFS Materialname BR BR BR BR Deterioration time (h)/ozone 1 1 7 — Deterioration time(h)/hot oxygen — — — 168 Contribution rate (%) of ozone deteriorationNot calculable 100 100 0 Contribution rate (%) of oxygen deteriorationNot calculable 0 0 100 Degree (%) of deterioration Not calculable 57 8819 Deterioration indicator Not calculable 0.22 0.43 0.40 ComparativeExample 3 Example 7 Example 8 Example 9 Measurement method XPS NEXAFSNEXAFS NEXAFS Material name SBR SBR SBR SBR Deterioration time (h)/ozone1 1 7 — Deterioration time (h)/hot oxygen — — — 168 Contribution rate(%) of ozone deterioration Not calculable 100 100 0 Contribution rate(%) of oxygen deterioration Not calculable 0 0 100 Degree (%) ofdeterioration Not calculable 12 37 5 Deterioration indicator Notcalculable 0.18 0.25 0.10 Comparative Example 4 Example 10 Example 11Measurement method XPS NEXAFS NEXAFS Material name IR/SIBS IR/SIBSIR/SIBS Deterioration time (h)/ozone 1 — 7 Deterioration time (h)/hotoxygen — 168 — Contribution rate (%) of ozone deterioration Notcalculable 0 100 Contribution rate (%) of oxygen deterioration Notcalculable 100 0 Degree (%) of deterioration Not calculable 16 85Deterioration indicator Not calculable 0.13 0.51 Example 12 Example 13Measurement method NEXAFS NEXAFS Material name Sample after driving inSample after driving in US Japan Deterioration time (h)/ozone — —Deterioration time (h)/hot oxygen — — Contribution rate (%) of ozonedeterioration 55 10 Contribution rate (%) of oxygen deterioration 45 90Degree (%) of deterioration 45 25 Deterioration indicator 0.63 0.21

In Comparative Examples 1 to 4 using XPS, none of the contribution ratesof ozone deterioration and oxygen deterioration, the degree ofdeterioration and the deterioration indicator (index) of thedeteriorated samples could be analyzed. In contrast, in examples usingNEXAFS, all of these items could be analyzed. The results shows that, inExamples 1, 2, 4, 5, 7, 8 and 11 subjected to only ozone deterioration,the contribution rate of ozone deterioration was 100%, and, in Examples3, 6, 9 and 10 subjected to only oxygen deterioration, the contributionrate of oxygen deterioration was 100%. Additionally, the results of thedegree of deterioration and the deterioration indicator in theseexamples had excellent correlations. In Examples 12 and 13 where samplessubjected to both ozone deterioration and oxygen deterioration wereused, the contribution rate of each deterioration could be analyzed.Therefore, the evaluation according to the present invention wasdemonstrated to be effective.

What is claimed is:
 1. A deterioration analysis method, comprising:irradiating a polymer material with high intensity X-rays, and measuringX-ray absorption while varying the energy of the X-rays, to analyzedeterioration of the polymer, wherein the polymer material is a rubbermaterial containing at least one diene rubber, or a composite materialcombining the rubber material and at least one resin, an energy rangescanned with the high intensity X-rays is 4000 eV or less, thedeterioration analysis method comprises: performing waveform separationof an X-ray absorption spectrum at the oxygen K-shell absorption edgeobtained by scanning over a range of high intensity X-ray energies of500 to 600 eV; and calculating contribution rates of oxygendeterioration and ozone deterioration using Equation 3 below, whereinthe oxygen deterioration corresponds to a peak on the low energy sidewith a peak top energy in the range of 532 to 532.7 eV, and the ozonedeterioration corresponds to a peak on the high energy side with a peaktop energy in the range of 532.7 to 534 eV:[peak area of oxygen deterioration]/[(peak area of ozonedeterioration)+(peak area of oxygen deterioration)]×100=contributionrate (%) of oxygen deterioration,and[peak area of ozone deterioration]/[(peak area of ozonedeterioration)+(peak area of oxygen deterioration)]×100=contributionrate (%) of ozone deterioration.   (Equation 3)
 2. The deteriorationanalysis method according to claim 1, wherein peak intensities are usedinstead of the peak areas.
 3. A deterioration analysis method,comprising: irradiating a polymer material with high intensity X-rays,and measuring X-ray absorption while varying the energy of the X-rays,to analyze deterioration of the polymer, wherein the polymer material isa rubber material containing at least one diene rubber, or a compositematerial combining the rubber material and at least one resin, an energyrange scanned with the high intensity X-rays is 4000 eV or less, thedeterioration analysis method comprises: determining a normalizationconstant γ using Equation 4 below based on an X-ray absorption spectrumat the carbon K-shell absorption edge after deterioration; andcorrecting a total peak area of the oxygen K-shell absorption edge withthe normalization constant γ based on Equation 5 below to determine theamount of oxygen and ozone bonded to the polymer material:[total area of X-ray absorption spectrum at carbon K-shell absorptionedge]×γ=1;and   (Equation 4)[peak area of oxygen K-shell absorption edge]×γ=amount (index) of oxygenand ozone bonded. (Equation 5)
 4. The deterioration analysis methodaccording to claim 1, wherein the high intensity X-rays have a number ofphotons of 10⁷ (photons/s) or more and a brilliance of 10¹⁰(photons/s/mrad²/mm²/0.1% bw) or more.
 5. The deterioration analysismethod according to claim 2, wherein the high intensity X-rays have anumber of photons of 10⁷ (photons/s) or more and a brilliance of 10¹⁰(photons/s/mrad²/mm²/0.1% bw) or more.
 6. The deterioration analysismethod according to claim 3, wherein the high intensity X-rays have anumber of photons of 10⁷ (photons/s) or more and a brilliance of 10¹⁰(photons/s/mrad²/mm²/0.1% bw) or more.